Entrance to catacombs is located on the square of fire and
settlement of klesva. To enter one needs a Torch, which can be bought at the mercenaries shop for 10 s
starting from level 5. Once a torch is lit you have access to the catacombs for
3 hours. In the first location you will find the bone
dragon and a bunch of nightmare umertniks. Later about them.

Transfer time in
catacombs is 1.5 minutes. You can make it faster by riding your steed, drinking
elixirs of speed, etc. Catacombs have 3 locations: Entrance, Dark Corridor, and
Forgotten library. Entrance has the nightmare umertniks, bone dragon, and the
stash. Corridor has nightmare umertniks, library also has umertniks, though much
less than the entrance or the corridor and guarantees you finding a pile of
papers once every 24 hours.

Now, let's talk about bots. Nightmare
umertniks cast Black Rage on you (converts 100% of their damage to hp.) can be
removed if you cast Black Eclipse on them. After that they just become a strong bot
with a lot of hp/crits/dodges, but nothing more than that. Don't forget that
chances are that more than one umertnik will join your fight, so either hit very
quickly, or have a few scrolls in your slots. On average they deal level 4-5
injuries for 14-17 hours.